Get the most from each lesson's compiled editor with a deliberate loop—the same habits that transfer to IntelliJ, VS Code, or CI pipelines running mvn test.
Recommended workflow
- Read the concept section before editing code.
- Click Run to compile and execute on the dev runner.
- Use
System.out.printlnfor readable output; print arrays withArrays.toStringwhen needed. - Change one idea at a time—a type, a loop bound, one method call.
- Read compile errors in stderr—often a missing semicolon, wrong type, or class name mismatch.
- Reset the editor if you drift far from the lesson goal.
What the runner can and cannot do
- Can — compile and run single-file
Mainprograms with standard library imports - Simulated — JDBC rows and Maven coordinates shown via
printlnmock data - Needs local setup — real MySQL via JDBC, multi-file Maven projects, Spring Boot servers
Review JavaScript functions and PHP classes if OOP terms feel unfamiliar.
Self-check
- Why must the public class be named
Mainin this playground? - What is the first step when you see a compile error?
Challenge
First compile and run
- Click Run with the default code.
- Confirm the Java version prints in the output.
- Add a second
printlnwith your name.
Done when: the terminal shows the Java version and your custom message.
Challenge
Verify compile output
- Run the default
Mainprogram. - Confirm Java version prints.
- Introduce a type error (assign a String to int) and read the compile message.
- Fix the error and run again.
Done when: you see a clear compile error when broken and successful output after fixing.